Possible Texas Bactrites

[BobWill]

I found this at the Lost Creek Dam site at Jacksboro Texas. It is the Finis Shale Member of the Graham Formatoion in the Upper Pennsylvanian Sub-period. I don't often find the apical end of any nautiloids so I was thinking it could help with the ID. There is a dark spot on the oral end that may or may not be the siphuncle, it is not clear. I thought it may be a Bactrites but it would be one without the hemispherical apex and constriction you see on some. It also has a cameral ratio higher than some Bartrites at around 3. I don't know what the black dots are.

 

 

 

 

 

[abyssunder]

I can't help you with an ID, but the specimen has very nice borings.

[BobWill]

12 minutes ago, abyssunder said:

I can't help you with an ID, but the specimen has very nice borings.

Is that what the black dots are? I will see if I can get a close-up of one.

[DPS Ammonite]

Black dots are probably clionid sponge borings that are filled with sediment or possible iron minerals.

 

See: http://woostergeologists.scotblogs.wooster.edu/tag/mississippi/page/2/

[BobWill]

These are the best I can manage for close-up pictures of the black dots.

 

 

[Manticocerasman]

hmm not clear on where the siphuncle is, if it is the black spot it is defenitly not a bactrites. Bactrites have a ventral siphuncle.

 

To be sure you'll need to slice a little part of the fossil to see if it is either a nautiloid  orthocone or a Bactrites sp. 

 

or just keep it at fossil orthocone

 

 

 

 

 

[abyssunder]

17 hours ago, BobWill said:

These are the best I can manage for close-up pictures of the black dots.

 

 

 

Yes, the little holes look like borings, probably belonging to Entobia.

..................................

Just crossed my mind the possibility of what is called "Housean  Pits ".

link

 

[Captcrunch227]

I'm no help on the id, but I can confirm that it's a gorgeous specimen!

[FossilDAWG]

I'm not sure the black spots are actually holes.  Bob could say for sure of course, but I don't see any shadow that would indicate they penetrate into the fossil.  I have seen incipient lichen type growing things on rocks that look like that.

 

As Manticocerasman said, the siphuncle in Bactrites is ventral.  Indeed it is right at the surface, you can see it as an elongated tube directly underneath the outer shell, lying on top of the suture lines.  I don't see anything like that on this specimen, but that might be because of the angle of the photos.

 

Don

[BobWill]

2 hours ago, FossilDAWG said:

I'm not sure the black spots are actually holes.  Bob could say for sure of course, but I don't see any shadow that would indicate they penetrate into the fossil.  I have seen incipient lichen type growing things on rocks that look like that.

 

As Manticocerasman said, the siphuncle in Bactrites is ventral.  Indeed it is right at the surface, you can see it as an elongated tube directly underneath the outer shell, lying on top of the suture lines.  I don't see anything like that on this specimen, but that might be because of the angle of the photos.

 

Don

Thanks Don. They do look a little more like something raised off the surface but I'll need better magnification to be sure.  I am trying to remove the matrix covering part of the oral end to see if the dark spot is really the siphuncle. This is too small to do easily so I may try to see if mild acid will help without damaging the fossil. Otherwise I may try to cut a slice into the end instead, Something about the missing sutures near the apical end made me think of Bactites but we may be seeing the external surface on that end.

[BobWill]

I exposed a little more of the end to see if the siphuncle would show better but this is all I got.

 

The round dark spot and the two white spots could be the siphuncle, or not, and I don't know if they would be too far from the margin but I have just read about some exceptions to the normal position. Turbobactrites eudorites  and Dilatobactrites missouriensis can be submarginal, removed by as much as 1/6th of the diameter from the venter and Globulobactrites loveladyensis n. gen., n. sp. is distinctly separated as well but I don't think this is any of those.